Mac and PC Compatible Cross-platform Portable Thunderbird 1.5 Revision 2
Portable Thunderbird is the popular Mozilla Thunderbird email program packaged as a cross-platform portable app, so you can take your email, drafts, cache, newsgroups, and saved passwords with you. It works on both Macs and PCs.

Read Me!
After you download the disk image or zip file containing the files that makeup the cross-platform Portable Thunderbird, expand them, then drag the "Portable Thunderbird" folder to the root directory (home) of your portable device (thumb drive, iPod, surgically implanted solid-state memory card, you name it as long as it has 42 megabytes of free space). That's it! Okay now, clicking PortableThunderbird.exe on a Windows computer will launch Thunderbird using the files in your portable profile. On a Mac, clicking "START OS X Thunderbird" will launch a script that makes your Windows portable Thunderbird profile folder compatible with Mac, and then it lauches Thunderbird using that profile. Now, due to a problem in my Mac OS X portable Thunderbird script, you might need to launch "START OS X Thunderbird" twice the very first time you download Portable Thunderbird.

Upgrading Thunderbird
Simply use Thunderbird's built-in updater to update Thunderbird (you will need to run it both on the Mac and Windows versions of Thunderbird if you want to update both).

How It Works (HIW)
Cross-platform Portable Thunderbird works by using John Haller's excellent Portable Thunderbird 1.5 on the Windows side of things, and a little script I made on the Mac side of things. The script basically changes your user profile every time you start Thunderbird so that it works on Mac and PC. The reason why is simple: as I am sure some of you have figured out, Windows Thunderbird profiles are not completely compatible with Mac Thunderbird, only certian files. So I made a script that keeps compatibility between Mac and PC, time consuming, I know, but it works.